Further SQL optimizations

src/pretix/base/migrations/0045_auto_20161108_1542.py

@@ -0,0 +1,30 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.10.2 on 2016-11-08 15:42
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0044_auto_20161101_1610'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='cartposition',
+            name='expires',
+            field=models.DateTimeField(db_index=True, verbose_name='Expiration date'),
+        ),
+        migrations.AlterField(
+            model_name='voucher',
+            name='redeemed',
+            field=models.BooleanField(db_index=True, default=False, verbose_name='Redeemed'),
+        ),
+        migrations.AlterField(
+            model_name='voucher',
+            name='valid_until',
+            field=models.DateTimeField(blank=True, db_index=True, null=True, verbose_name='Valid until'),
+        ),
+    ]

src/pretix/base/models/items.py

@@ -582,7 +582,7 @@ class Quota(LoggedModel):
             Q(redeemed=False) &
             Q(Q(valid_until__isnull=True) | Q(valid_until__gte=now_dt)) &
             Q(Q(self._position_lookup) | Q(quota=self))
-        ).distinct().count()
+        ).values('id').distinct().count()
 
     def count_in_cart(self, now_dt: datetime=None) -> int:
         from pretix.base.models import CartPosition
@@ -595,21 +595,22 @@ class Quota(LoggedModel):
                 & Q(Q(voucher__valid_until__isnull=True) | Q(voucher__valid_until__gte=now_dt))
             ) &
             self._position_lookup
-        ).distinct().count()
+        ).values('id').distinct().count()
 
     def count_pending_orders(self) -> dict:
         from pretix.base.models import Order, OrderPosition
 
+        # This query has beeen benchmarked against a Count('id', distinct=True) aggregate and won by a small margin.
         return OrderPosition.objects.filter(
             self._position_lookup, order__status=Order.STATUS_PENDING,
-        ).distinct().count()
+        ).values('id').distinct().count()
 
     def count_paid_orders(self):
         from pretix.base.models import Order, OrderPosition
 
         return OrderPosition.objects.filter(
             self._position_lookup, order__status=Order.STATUS_PAID
-        ).distinct().count()
+        ).values('id').distinct().count()
 
     @cached_property
     def _position_lookup(self) -> Q:

src/pretix/base/models/orders.py

@@ -515,7 +515,8 @@ class CartPosition(AbstractPosition):
         auto_now_add=True
     )
     expires = models.DateTimeField(
-        verbose_name=_("Expiration date")
+        verbose_name=_("Expiration date"),
+        db_index=True
     )
 
     class Meta:

src/pretix/base/models/vouchers.py

@@ -70,10 +70,11 @@ class Voucher(LoggedModel):
     )
     redeemed = models.BooleanField(
         verbose_name=_("Redeemed"),
-        default=False
+        default=False,
+        db_index=True
     )
     valid_until = models.DateTimeField(
-        blank=True, null=True,
+        blank=True, null=True, db_index=True,
         verbose_name=_("Valid until")
     )
     block_quota = models.BooleanField(

src/pretix/base/payment.py

@@ -4,7 +4,6 @@ from typing import Any, Dict
 
 from django import forms
 from django.contrib import messages
-from django.db.models import Sum
 from django.dispatch import receiver
 from django.forms import Form
 from django.http import HttpRequest
@@ -13,9 +12,10 @@ from django.utils.translation import ugettext_lazy as _
 
 from pretix.base.decimal import round_decimal
 from pretix.base.i18n import I18nFormField, I18nTextarea, LazyI18nString
-from pretix.base.models import CartPosition, Event, Order, Quota
+from pretix.base.models import Event, Order, Quota
 from pretix.base.settings import SettingsSandbox
 from pretix.base.signals import register_payment_providers
+from pretix.presale.views import get_cart_total
 
 
 class BasePaymentProvider:
@@ -503,9 +503,7 @@ class FreeOrderProvider(BasePaymentProvider):
         messages.success(request, _('The order has been marked as refunded.'))
 
     def is_allowed(self, request: HttpRequest) -> bool:
-        return CartPosition.objects.filter(
-            cart_id=request.session.session_key, event=request.event
-        ).aggregate(sum=Sum('price'))['sum'] == 0
+        return get_cart_total(request) == 0
 
     def order_change_allowed(self, order: Order) -> bool:
         return False